Step 4, 5, & 6 are not necessary for this bug to break stuff, but it's more fun that way.

Guest Type does not matter, will crash everything from Windows 6.2 to Bimbo's Linux

I have only tested this where the host machine is Linux (kali), not sure if the same bug is present when host is another OS, although I would venture to assume so.

Qt WARNING: QFileInfo::absolutePath: Constructed with empty filename
This is a bug. Maybe you can fix it so that when you accidentally type a / in the name field of a new machine, you don't crash every freaking running VM... Just a thought. Perhaps, yeah? You can fix? Okay vunderbar

Change History

A critical error has occurred while running the virtual machine and the machine execution should be stopped.

For help, please see the Community section on https://www.virtualbox.org or your support contract. Please provide the contents of the log file VBox.log, which you can find in the virtual machine log directory, as well as a description of what you were doing when this error happened. Note that you can also access the above file by selecting Show Log from the Machine menu of the main VirtualBox window.

WOW... confirmed. Clearly an API bug, but I wonder why the GUI makes the failing API call straight after typing in / - I see no reason for that right now, but maybe looking at the GUI code will tell more.